1. Field of the Invention
The present invention relates to an apparatus for manufacturing polycrystalline silicon which manufactures rods of polycrystalline silicon by depositing polycrystalline silicon on surfaces of heated silicon seed rods.
Priority is claimed on Japanese Patent Application No. 2009-56057, filed Mar. 10, 2009, the content of which is incorporated herein by reference.
2. Description of the Related Art
Generally, the Siemens process is known as a manufacturing method of high-purity polycrystalline silicon for semiconductor. The Siemens process is a manufacturing method in which raw-material gas including mixed gas of chlorosilane and hydrogen is in contact with heated silicon seed rods so that polycrystalline silicon generated by thermal decomposition and hydrogen reduction of the raw-material gas is deposited on the surfaces of the silicon seed rods. As an apparatus for carrying out the manufacturing method, a polycrystalline silicon reactor is used in which a plurality of silicon seed rods (i.e., starter filaments) are mounted on electrodes which are installed on a reactor floor of the closed reactor (refer to Japanese Unexamined Patent Application, First Publication No. H05-213697).
Conventionally, in the reactor, a seed assembly which is formed into a Π-shape from two rod-like silicon seed rods provided along the vertical direction and a connecting member which connects the top ends of the silicon seed rods are fixed. The seed assembly is highly-heated by being supplied electricity via the electrodes so that Joule heat is generated.
The silicon seed rod is manufactured, for example, by method of drawing up single crystal from melted silicon and making into an elongated silicon seed rod, or by cutting a polycrystalline silicon preform produced by the Siemens process.
By the former method, comparatively straight cylindrical silicon seed rods can be obtained. However, manufacturing efficiency is low since a monocrystalline silicon rod requires long time to be produced.
On the other, by the latter method, high-purity silicon seed rods can be obtained since the silicon seed rods are cut from a high-purity polycrystalline silicon preform (e.g., a rod-shape). However, there is a case in which thermal stress is generated in the polycrystalline silicon rods produced by the Siemens process in the producing process, for example, as described in PCT International Publication WO97/44277, so that the silicon seed rods might be bended after cutting.
In the process of depositing polycrystalline silicon on the surfaces of the silicon seed rods by reacting of raw-material gas in the reactor, the weight of the polycrystalline silicon deposited on the surfaces of the silicon seed rods reaches several ten kilograms after continuous reaction. If the silicon seed rods holding the polycrystalline silicon are bended, the electrodes or the silicon seed rods are easily broken by the weight of the deposited polycrystalline silicon. Further, since the plurality of silicon seed rods are vertically arranged in the reactor, the intervals between the silicon seed rods are not even if the silicon seed rods are bended, so that the silicon seed rods are overheated at adjacent parts with each other by the radiation heat thereof. Therefore, the deposition amounts of the polycrystalline silicon are not even by position, then the polycrystalline silicon deposits unevenly, so that the product quality may be deteriorated. Therefore, it is preferable that the silicon seed rods in the reactor stand vertically.
Therefore, the deformations of the silicon seed rods are corrected so as to erect the silicon seed rods, in a pair of silicon seed rods which are connected to each other, by attaching the connecting member in a state in which the silicon seed rods are fixed after adjusting the bending direction thereof. However, there is a case in which the silicon seed rods are hard to erect by only adjusting the bending direction of the silicon seed rods and attaching the connecting member. In this case, the connecting member is attached again; and the silicon seed rods are rotated and fixed again. However, those tasks delay the manufacturing, so that the productivity is deteriorated. Furthermore, the silicon seed rods may be broken with high-probability during those tasks since the plurality of seed assemblies are arranged. Moreover, the tasks take time so that the silicon seed rods are exposed to air for a long time; then the probability of contamination on the surfaces of the silicon seed rods may become high.